Many modern day bone cements of the two component powder/liquid type are known which, when thoroughly mixed together, undergo polymerization thereby forming a hard and more or less durable cement mass.
While the present invention can be used to prepare a variety of such cements, it is especially useful in the preparation of so-called bone cement used to anchor and support artificial joint components and other prostheses in natural bone. Accordingly, it will be described here specifically in that context.
The currently preferred bone cement is polymethylmethacrylate or so-called PMMA. PMMA is comprised of a powdered polymer and a liquid monomer. Upon mixing, these components polymerize within minutes so as to form a firm rigid bond between the prosthesis and the surrounding bone structure in which the prosthesis is placed.
The present procedure for preparing PMMA bone cement is to thoroughly mix the powder and liquid component in order to start polymerization whereby the cement mass turns to a putty or dough consistency. The partially cured cement is then applied to the bone structure to be treated, e.g. into the medullary canal of the femur which is receiving a femoral shaft of a hip joint prosthesis.
All known methods for mixing bone cement have serious drawbacks, the most essential being:
poor mixing, which depends on the individual mixing technique; PA1 high exotherm, due to the considerable amount of liquid component necessary to produce an applicable cement mass by conventional mixing techniques; PA1 creation of porosities by inclusion and entrapment of air bubbles as well as by evaporation of excess monomer resulting in significant degradation of the mechanical properties of the cured cement.